1. Field of the Invention
The invention relates to a multilayer plastic pipe comprising at least five layers adhesively bonded to each other.
2. Background of the Invention
Plastic pipes made from polyamide have previously been employed for a variety of applications. It is known that in order to achieve their objective, the pipes must be, inter alia, inert to the medium flowing in them, and must be resistant to high and low temperatures and mechanical stresses.
Single-layer pipes are not always capable of satisfying the necessary requirements. In the case of transport of, for example, aliphatic or aromatic solvents, fuels or the like, they exhibit considerable disadvantages, such as a poor barrier action to the medium, undesired changes in dimension or inadequate resistance to mechanical stresses.
Attempts to overcome these disadvantages have included the use of multilayer pipes (DE-A 35 10 395; DE-A 37 15 251; DE-A 38 21 723; DE-A 40 01 125 and DE-A 40 01 126). However, practical implementation of these proposals has shown that, although some disadvantages can be overcome, the overall property profile is still unsatisfactory.
French Patent 2 602 515 describes a two-layer pipe comprising an outer layer of nylon 11 and an inner layer of plasticized polyvinylidene fluoride. However, investigations have shown that the barrier action to the flowing medium is unsatisfactory.
German Patent 38 27 092 describes a multilayer plastic pipe which comprises, from the inside outwards, layers of polyamide, polyvinyl alcohol, polyamide and polyester. The polyester is only used in a thin outer layer so as to achieve higher short-term heat deformation resistance. Further, it is known to those skilled in the art that by far the majority of polymers, including polyamides and polyesters, are incompatible with one another, since no adhesion is achieved between the laminate layers in the production of multilayer composites. An adhesive bond between the individual polymer layers is absolutely essential in industrial applications, however.
In particular, permeation of methanol-containing fuels has only been reduced to an inadequate extent by means of the abovementioned proposals.
Reduction in permeation by using novel intermediate layers is therefore of crucial importance because, in particular, the legally permitted emission values are constantly being reduced.